THC is an acronym for Tetrahydrocannabinol. The 2018 Farm Bill explicitly defined 'THC' as 'delta-9 THC' under United States Federal law. There are, however, several THCs (and I do not mean delta-9 THC isomers). Delta-8 THC is an example of another 'THC' that is not technically illegal under the 2018 Farm Bill. (Under the 2018 Farm Bill, so long as they are made from Industrial Hemp with under 0.3% 'THC' (delta-9 THC), extracts and products will not be under the purview of the controlled substance act - i.e. the DEA. (Or something along those lines. This is not legal advice!)
Delta-8 THC does get you high! The effects are similar but not identical to delta-9 THC. Wikipedia is a great source of information and we encourage you to read further there. In short, delta-8 THC has similar effects as delta-9 THC but is not as potent and does not last as long. And it is usually less expensive for very similar effects!
For most things that people use delta-9 THC for delta-8 THC could be used instead. For example, antiemetics (anti-nausea, hangovers), anxiety, relaxing, pain management and aid with sleep seem to be some of the more common self-medicating uses for delta-8 THC. Recreational uses would be general euphoria, relaxing and increased sensory experience and pleasure (MUCNHIES!). Everybody's experience is different though!